Control circuit



March 1961 w. E. GREEN EI'AL 2,977,039

CONTROL CIRCUIT Filed July 10, 1958 2 Sheets-Sheet 1 FIG. 1.

F E J. 6 l7 C 40 INVENTORS.

ERNEST H. STARK WILLARD E. GREEN L WW ATTORNEY 2 Sheets$heet 2 30 A Y U\RKFM.

CONTROL CIRCUIT W. E. GREEN EI'AL March 28, 1961 Filed July 10, 1958INVENTORSZ WILLARD E. GREEN BY ERNEST H. STARK ZZZ/ W ATTORNEY gg k V unsd W8 Pa ent .0

2,977,039 CONTROL CIRCUIT Willard E. Green, Olean, N.Y., and Ernest H.Stark, Michigan City, Ind., assignors to Joy Manufacturing Company,Pittsburgh, Pa., a corporation of Pennsyl- Vania Filed July 10, 1958,Ser. No. 747,784 13 Claims. (Cl. 230-2) This invention relates to acontrol circuit and more particularly to a fiuid control circuit forisolating a rotary compressor from its receiver.

In the art of rotary compressors it is common practice to discharge thehigh pressure medium directly to a receiver from which the high pressuremedium is drawn as needed. Where there is a steady demand for thecompressed medium the compressor continues to discharge the highpressure medium to the receiver. Underconditions of small or no demandfor the compressed medium no compressed-medium is drawn from thereceiver and the high pressure ofthe receiver is exerted against thehigh pressure stage of the compressor. As can readily be appreciatedmore energy is required to drive the compressor against the receiverpressure than is required to drive the compressor against a pressuresubstantially lower than the receiver pressure. Heretofore with rotarycompressors driven by a variable speed prime mover, suchas a gasoline ordiesel engine, it is possible to reduce the energy consumption of theprime mover by merely reducing its speed in some suitable manner such asthat shown in the copencling application of Willard Green, entitledControl Device, Serial No. 699,838, filed November 29 1957, whichapplication hasbeen assigned to the same assignee as-the assignee ofthis invention. In other rotary compressors in which the rotatingelements are driven by a constant speed prime mover, such as an electricmotor, no means heretofore have been' provided for reducing the energyrequirements of the compressor during its unloaded condition. As canreadily be appreciated such isolation of the receiver must bediscontinued upon increased demand of the compressed medium and from apractical commercial standpoint such isolation and non-isolation mustoccur automatically to insure efiicient operation of the compressor anda sufficient supply of the compressed medium.

Accordingly one object of this invention is to provide a new andimproved control circuit for a rotary compressor for isolating thecompressor from its receiver when there is little or no demand forcompressed medium and for discontinuing such isolation upon increaseddemand for the compressed medium.

Another object of this invention is to provide a new and improvedcontrol circuit for a rotary compressor for isolating the compressorfrom its receiver which employs the changes in pressure-in anintermediate receiver of the compressor to obtain such-isolation.

'A specific object of this invention is to provide a new and improvedcontrol circuit for a rotary compressor forisolating the compressor fromits receiver which obtains, such isolation in response to positive andnegative 1,

ice

pressures existing in an intermediate receiver of the compressor. VThese and other objects of this invention will become more apparent uponconsideration of the following detailed description of a preferredembodiment thereof, when taken in conjunction with the followingdrawings, in which: 1

Fig. 1 is a cross section view including the inlet and discharge valvestherefor of a typical rotary compressor which a circuit constructed inaccordance with the principles of this'invention is adapted to control,and Fig. 2 is a diagrammatic representation of a rotary compressor,receiver, and auxiliary equipment connected together by a controlcircuit constructed in accordance with the principles of this invention.

In the description of this invention air has been employed as themedium'compressed by the compressor; however, it is to be realized thatsuch use of air is for convenience only and that the principles of thisinvention are equally applicable to all types of compressor fluids.Referring .to Fig. 1 of the drawings it will be noted that a rotarycompressor 1 of a construction which isadapted to be controlled by acontrol circuit of this invention comprises a suitable formed housing 2having a vane supporting 'first stage rotor 4 which initially com'presses air admitted through an open inlet valve 6 from atmosphericpressure to an intermediate pressure. Such initially compressed air isdischarged from the first stage rotor 4 through an opening 8 in thehousing 2 through an intermediate receiver 10 formed integrally by thehousing 2. Thereafter the initially compressed air is admitted throughan'opening 11 in the housing 2 into a vane supporting second stage rotor12 wherein it is further compressed to a desired final, high pressure.The

high pressure air is then discharged from the second stage is connectedto a receiver 20. Inasmuch as the structure of such a rotary compressor1, inlet and outlet valves, and receivers are well known in the art anddo not constitute a part of this invention further descriptionthereof isnot believed to be warranted.

As is customary the inlet valve 6 is provided with a valve head 5 whichis movable into a closed position, as shown, so that no air can beadmitted to the first stage rotor 4. Similarly the discharge valve isprovided with a valve head 17, shown open, which is biased at all timesby means of a suitable spring 22 towards its closed position. Undernormal or loaded operating conditions, the second stage rotor 12discharges high pressure air against the valve head 17 to overcome thebias of the spring 22 to open and hold the discharge valve 16 in itsopen position.

The control circuit of this invention depends upon the followingoperating characteristic of a constant speed rotary compressor. When theinlet valve 6 is closed the rotors 4 and 12 continue to rotate at aconstant speed and, since no air is supplied to the first stage rotor 4,the rotation of the rotor 4 createsa vacuum in the space between theclosed inlet valve 6 and the inlet of the rotor 4 which vacuum passesprogressively through the compressor as the continually rotating secondstage rotor 12 causes the intermedia eteceiyer 10in turn to. beevacuated-which is sensed by line D in valve 100. When the receiver 20remains connected to the discharge connection 15 the rotor 12 mustcontinue to operate against the receiver pressure on its discharge sidewhile a vacuum exists on its inlet side. The following pressureconditions of a rotary compressor under normal operating conditions havebeen setfor the purpose of illustration only. The first stage rotor 4compresses air from atmospheric pressure to an intermediate pressure of30 lbs. per square inch gauge in the intermediate receiver 10 and thesecond stage rotor 14 compresses the intermediate receiver air from 30lbs. per square inch gauge to 100 lbs. per square; inch gauge. In viewof the fact that the air discharged from the rotor 12 holds thedischarge valve 16 open the receiver 20 is normally .at a pressure of100 lbs. per square inch gauge. With the :inlet valve 6 closed the samecompressor has a vacuum of l to l2 .lbs. per square inch gauge in .theintermediate receiver and the second stage rotor '12 operates :between avacuum of l0 lbs. per square :inch gauge to l2 lbs. per square inchgauge on its inlet side to 100 lbs. per square inch gauge on itsdischarge side. In addition it should be borne in mind that incompressors of this type oil is normally injected into the air flowingthrough the compressor to provide for lubrication of and a sealingmedium on the vanes of the rotors 4 and 12 and also to absorb the heatof the compression. Accordingly, such injected oil is discharged fromthe second stage rotor 12 to the receiver 20.

Referring to Fig. 2 it will be noted that the rotary compr'essor 1 shownin and described with relation to Fig. 1 has been shown diagrammaticallytherein. As is customary with the receiver 20, the inlet line 18 extendsin wardly thereof to cause the majority of the oil discharged therein tocollect at the bottom of the receiver 20.. Although not shown it is tobe realized that even the most eflicient oil separating means does notremove all oil from the line 18 so that some high pressure air havingoil entrained therein is also contained in the receiver 20 above the oilin the bottom of the receiver 20. In order to limit the amount of oilused in the compressor 1 a suitable oil flow line B is connected betweenthe oil collecting portion or sump of the receiver 20 and to a novelcontrol valve 100 the structure of which is more fully shown, describedand claimed in Serial No. 747,725, filed July 10, 1958, entitled ControlDevice by Ernest H. Stark which application has been assigned to thesame assignee as this invention. As will become apparent upon reviewingthe above identified copending application the letterdesignation of thevarious fluid transmission lines connected to the control valve 100 inthis application have been given the same letter designation as thefluid transmission lines in the above identified copending applicationso that ready comparison may be made there- 7 between. The valve 100 isprovided with an exit line A which is connected to the line B undernormal operating conditions of the compressor.

The line A is connected to a thermal bypass valve 24 which has an exitline 26 connected thereto with the remote end of the line 26 beingconnected to a suitable oil pump 28. The oil pump 28 is provided for thepurpose of both lubricating the compressor and injecting oil into theair flowing therethrough. In addition the oil pump 28 may be employed tolubricate a driving means 7 which is connected to the rotary compressorto cause rotation thereof as is well known in the art. has much as theinternal structure of the compressor and the drive means 7 for obtainingsuch lubrication and injection of oil is well known'in the art theparticular description thereof is not believed to be necessary. It willbe noted, however, that the oil pump 28 is provided with a suitabledischarge line 31 connected to the compressor 1.

The structure of the bypass valve 24 is well known in theart and doesnot constitute a part of this invention.

As is well known when the injected oil is cold, as during the initialstarting of the compressor 1, oil flows from line A to line 26, so as tobe immediately circulated through the valve 24'. After operation of thecompressor 1 the oil collected in the receiver 20 which has been heatedand the bypass valve, by means of a suitable thermal device actuated bythe flow of heated oil therearound, disconnects the low resistance lineA from the line 26. When the line A and the line 26 are so disconnected,the oil from the line A flows through a suitable fluid transmitting line30 having a suitable filter 32 and a radiator 34 therein as are wellknown in the art to a portion of the bypass valve 24 to permit flowtherethrough to the line 26. With such .a thermally controlled alternatepath for the heated oil the heat of the oil may readily' be removed soas to insure its ability to absorb the heat ofthe compression in amanner as well known in the art.

The oil entrained in the oil-air mixture in the receiver 20 is alsoemployed to lubricate. portions of {the compressor sequentially locatedafter the intermediate receiver 10. Accordingly the air-oil mixtureportion of the receiver 20 is connected by a suitable line H through avalve 52 to a line G the other end of which is connected to theintermediate receiver it). Such connections and lines as the otherconnections and lines heretofore and hereinafter described may be madein any suitable manner as is well known in the art. The valve 10!)connects the line H to the line G when the compressor is running loadedas is shown in Figure 3 and more fully described in the latteridentified copeudiu'g application. As indicated the compressor isisolated from the receiver 26 in response to pressure diflerencesoccurring in the interrncdiate receiver 10. Accordingly the intermediatereceiver 10 is; connected to a chamber 130 in the valve by means of asuitable line D so that when the compressor 1 is operated to dischargecompressed air the line B is connected to the line -A and line H isconnected to the line G as is clearly shown by Fig. 3. Thus reciprocablepiston 122 mounted in bore 106 of control valve 100 is biasedrightwardly communicating line B with line A as shown in Fig. 3.

When the inlet valve 6 of the compressor is closed and a vacuum createdin the intermediate receiver '10 such vacuum is transmitted through aline Dto the chamber of the valve 100 to thereby sense the fall inpressure and thereby cause operation of the valve "100 to an unloadedposition so that the discharge lines B and H from the receiver 20 areclosed. As shown in phantom lines in Fig. 3, the piston 122 will moveleftward since a vacuum is created in chamber through line D whereas theright side of piston 122 and chamber 130 is connected to atmosphere viaconduit 136 to thereby force the piston 122 in the direction of thevacuum. In order to obtain complete isolation of the receiver from thecompressor it is also necessary to close the discharge valve 16 so thatthe pressure from the receiver 20 cannot be exerted against the secondstage rotor 12. Such complete isolation of the receiver 20 is obtainedby having the valve 100 when moved to an unloaded position as shown inphantom lines in Fig. 3 actuate an auxiliary valve 54 whereby a controlline F is connected to a vent line B. This is accomplished by piston122-striking a plunger upon leftward movement of the piston 170 whereinthe plunger 170 unseats a spring loaded ball valve 16% therebycommunicating control line F to vent line B. The operation of anauxiliary valve 50 and 52 of the valve 100 are more fully shown,described and claimed in the latter identified copending application. Asshown in Fig. l the line F is connected between the discharge connection15 and the auxiliary valve 50 and the line E is connected betweenanother portion of the auxiliary valve 50 and passageway 36 (Fig. 1')extending through the discharge valve 16. The end of the passageway 36remote from the line Eis connected to "a suitable line 6% eta-rag a Itwill be realized that when the valve 100 is moved from its normal loadedposition when the compressoris discharging high pressure air to thereceiver 20 to its alternative unloaded position shown in phantom linesin Fig. 3 when the compressor is disconnectedfrom the receiver 20, thehigh discharge pressure of the second stage rotor 12 exists in thedischarge connection 15 which high pressure is transmitted by thelines Fand ,E to the passageway 36. Thereafter. the high pressure air inpassageway 36 is ventedslowly to atmosphere by means of the line 40through the restrictive fitting 38. As is well known in the art,;'the,restrictive fitting in the end of the line 40 remote from the valve-16,does'not permit the pressure in the line 40a; collapse to atmospherebut bleeds the pressure in line 40' slowly' to atmosphere.Accordinglyyduring the time increment that line 40. is beingbled toatmosphere the oil pressurewhich exists in the discharge connection 15also exists inthe passageway 36. In view ofthe fact that the flowthrough the line 40 normally comprises a mixture of oil and air'suchoil-air mixture is bled into the housing of the dr'ive means 7 which isprovided with a breather, as 'is well known in the art, to permit thepressure withinthe housing to escape to atmosphere. Such a structurepermits the oil from the line 40 to collect in the bottom of the housingfor the drive means 7 where it can be removed therefrom by means of asump line 29 connected to the pump 28.

As shown in Fig. 1 such high pressure in the passageway 36 is directedagainst a plunger portion 17 of'the discharge valve which force inconjunction with the bias of the spring 22 moves the discharge valve 16to a closed position in a manner as is well 'knowninthe art. As thedischarge valve 16 is normally held openby air from the receiver isexerted against downstream side of the discharge valve 16 to hold thedischarge valve in its closed position. Since the receiver 20 is nowdisconnected from the discharge connection 15 the discharge lines F andE, passageway 36, and line 40 from the discharge connection 15 slowlybleed the pressure from the :discharge' connection 15 to atmospherewhich low pressure condition will prevail therein as long as thedischarge valve' 16 remains closed.

It will be'realized, however, that with the rotors 4 and 12 constantlyrotating it is necessary to provide some means for discharging the oilinjected into the compressor. Accordingly it will be noted that an oilflow line C is connected to the discharge connection 15 and .to thefvalve 100 so that when the valve 100 moves to close the lines B andH,'the line C is connected to line A. Since lthelineC is so connected tothe line A the oil may circulate through the same circuitry asheretofore described with relation to the oil from the line B. It will"be realized that since the pressure within the discharge connection 15is dropped due to the vent line 40, when 'the discharge valve 16 isclosed, the pressure in the line .C' and the line A will drop inaccordance with'the pressure in the discharge connection 15. Byreferring to the latter identified copending application, it will berealized that such pressure drop in the valve'100 is employed to .loclethe discharge valve 100 in its unloaded position.

I Should the demand for air from the receiver 20 increase the inletvalve 6 is'opened to permit air to flow through the compressor. Such airflow through the compressor causes the vacuum in the intermediatereceiver -10 to be destroyed whereby the intermediate pressure in theintermediate receiver 10 is again created. Such :pressure is transmittedthrough the line D to the valve I;100'. which is of a structure to causethe valve 100 to zmove to its normal pperating position since thepressure created in line D will force the'piston' 122 rightward to-.wardits loaded position shown in full lines in Fig. 3

-wbereat the line F i di conne ed o t e n m grai e 5 3 F ui y line .C isconcurrently, disconnected from line A.. Coricurrently, the line B isagain connected to line A and line H is again connected to line G.

Thus it will be noted that this invention has provided an automaticmeans for isolating the receiver from the compressor when no demand forair from the receiver '20 occurs while also automatically returning thepressure to the receiver 20 when the demand for air from the receiverincreases; Having described a preferred embodiment of this invention inaccordance with the patent statutes, it is to be realized thatmodifications thereof may be made without departing from the broadspirit and scope of the invention. Accordingly it is respectfullyrequested that this invention be interpreted as broadly as possible andbe limited only by the prior art.

Whatwe claim is: 3

1. A' control circuit for isolating a compressor having 'a dischargeline with a high pressure medium flowing therethrough, a control means,a control line connecting How therethrough upon closure' thereof thepressure said control'means and said discharge line, a vent lineoperatively connected to said control line by said control means whereinsaid vent line has a means at a portion thereof'remote from said controlmeans to slowly vent the pressure therein to a lower pressure, said ventline having means intermediate said control means and said portionthereof connected to said discharge linefor closing said discharge linein responseto flow of a pressurized medium therethrough at a pressureabove said lower pressure while flow through said control linecontinues, and said control means connecting said control line to saidvent vline when said means intermediate said control means and saidportion thereof is actuated to close said discharge line. i

2. A control circuit for isolating a compressor having an inlet andoutlet with said outlet connected to a discharge linewith a highpressure medium flowing therethrough,' a control valve operativelyconnected to said discharge line, a control line connecting said controlvalve to said discharge'line, a vent line operatively connected to saidcontrol line by said control valve wherein said vent line has dischargemeans at a portion thereof remotefrom said control valve wherebypressure medium in said vent line is slowly vented to a lower pressure,

said vent line having valve means intermediate said control valve andsaid discharge means connected to said discharge line for closing saiddischarge line in response to 'flow of a pressurized medium therethroughat a pressure above said lower pressure without aflecting flow through'said control line, and a sensing line connecting said control valve'toa portion of said compressor intermediate said inlet and said outlet foroperating said discharge line operative in one condition to cause saidcontrol valve to communicate said control line and said'vent line.

3. A control circuit for isolating a multl-stage compressor wherein saidcompressor has an inlet and outlet with said outlet being connected to adischarge line having a high pressure medium flowing therethrough, acontrol valve, a control line connecting said control valvewithoutaitecting flow through said control line, sensing means connectedto an intermediate receiver portion of said compressor and tosaidcontrol valve to causesaid control valve to; condition said controlline and said'vent line into communicative relationship in response tovariations in the pressure in said intermediate portion above and belowatmospheric pressure resulting from the clos- 4. A control circuit forisolating a multi-stage compressor wherein said compressor is connectedto a discharge line having a high pressure medium flowing therethroughto a receiver, a control valve operatively connected at one end to saiddischarge line through said receiver, a control line connected to theother end of said control valve, a vent line operatively connected tosaid control line by said control valve wherein said vent line has adischarge means at a portion thereof remote from said control valvewhereby the pressure in said vent line is slowly vented to a lowerpressure, said vent line having valve means intermediate said controlvalve and said discharge means connected to said discharge line forclosing said discharge line in response to flow of a pressurized mediumtherethrough at a pressure above said lower pressure without affectingflow through said con trol line, sensing means connected to anintermediate receiver portion of said compressor and to said controlvalve to cause said control valve to connect said vent line to saidcontrol line in one position to connect said control line to said ventline, and to thereby cause said valve means to be subjected to thepressurized medium in said receiver to bias said valve means into closedposition.

5. A control circuit for isolating a multi-stage compressor having aninlet and outlet with said outlet being connected to a discharge linehaving a high pressure medium flowing therethrough, a control valvehaving two difierent operating positions resulting from the opening orclosing of said inlet, a control line connected to said discharge lineand to said control valve, a vent line operatively connected to saidcontrol line by said control valve wherein said vent line has dischargemeans at a portion thereof remote from said control valve whereby thepressure therein is slowly vented to a lower pressure,

said vent line having valve means intermediate said control valve andsaid discharge means connected to said discharge line for closing saiddischarge line in response to flow of a pressurized medium therethroughat a pressure above said lower pressure without afiecting flow throughsaid control line, and said control valve blocking said control linefrom being connected to any other lines when said control valve is inone position, and for connecting said control line to said vent linewhen said control valve is in its second position.

6. A control circuit for isolating a multi-stage compressor having aninlet and outlet, a discharge line connecting said outlet to a receiver,said receiver having an oil sump therein, a control valve connected tosaid discharge line through said receiver, sensing means connected to aportion of said compressor intermediate said inlet and outlet and tosaid valve to cause said control valve to assume a first or a secondposition in response to pressure variations in said intermediate portionresulting from a corresponding opening or closing of said. inlet, afirst oil flow line connecting said control valve and said oil sump, asecond oil flow line connecting said discharge line to said valve, saidvalve having an oil flow exit line, a control line connected to saiddischarge line and to said valve, a vent line operatively connected tosaid control line by said valve wherein said vent line has dischargemeans remote from said valve whereby the pressure therein is slowlyvented to a lower pressure, said vent line having means intermediatesaid valve and said discharge means connected to said discharge line forclosing said discharge line in response to flow of a pressurized mediumtherethrough at a pressure above said lower pressure without afiectingflow through said control line and said second oil flow line, said valvein said first position connecting said first oil flow line to said oilexit line and preventing said control line and second oil flow linesfrom being connected to any other lines when said inlet, is open, andsaid valve in said second position connecting said second flow line tosaid on exit line and said control line to said vent line and preventingV 8 said first oilflow line from being connected to any other line whensaid inlet is closed.

7. A control circuit for isolating a multi-stage compressor "having aninlet and outlet, a discharge line con necting said outlet to areceiver, said receiver having an oil sump therein, a control valve'connectedjto said discharge line through said receiver, sensing meanscon nected to a portion of said compressor intermediate said inlet andoutlet and to said control valve to causesaid control valve to assume afirst position or a second posi tion in response to pressure variationsin said intermediate portion resulting from a corresponding opening orclosing of said'inlet, a first oil flow line connecting said valve andsaid oil sump, a second oil flow line connectingsaid discharge line tosaid control valve, said control'valve having an oil flow exitline, acontrol line connected to said discharge line and to said control valve,a vent line operatively connected to said control line by said controlvalve wherein said vent line has a restrictive opening at the endthereof remote from said valve whereby the pressure therein is slowlyvented to a lower pressure, said vent line having valve meansintermediate said control valve and said restrictive opening connectedto said discharge line for closing said discharge line in response toflow of a pressurized medium therethrough at a pressure above said lowerpressure without afiecting flow through said control line and saidsecond oil flow line, said control valve in said first positionconnecting said first oil flow line to said oil exit line and blockingsaid control and second oil flow lines irom being connected to any otherlines when said inlet is open, said control valve in said secondposition connecting said second flow line to said oil exit line and saidcontrol line to said vent line and blocking said first oil flow linefrom being connected to any other line when said inlet is closed andsaid valve means for closing said discharge'line having an areasubjected to the pressurized medium in said receiver to bias said valvemeans for closing into its closed position.

8. A control circuit for isolating a multi-stage compressor having aninlet and outlet, a discharge line connecting said outlet to a receiver,said receiver having an oil sump therein, a control valve connected tosaid discharge line through said receiver by a first oil flow lineconnecting said oil sump and control valve, sensing means connected toan intermediate receiver portion of said compressor and to said valve tocause movement of said valve in response to variations in the pressurein said intermediate portion above and below atmospheric pressureresulting from the opening or closing of said inlet, a second oil flowline connecting said discharge line to said valve, an oil flow exit lineconnecting said valve to oil injecting means, said oil injecting meansoperatively connected to said compressor for injecting oil into saidcompressor, a control line connected to said discharge line and to said,valve, a vent line operatively connected to said control line by saidvalve wherein said vent line has restriction means in a portion thereofremote from said valve whereby the pressure therein is slowly vented tothe atmosphere, said vent line having means intermediate saidrestriction means and said valve connected to said discharge line forclosing said discharge line in response to flow of a pressurized mediumtherethrough at a pressure above atmospheric pressure Without affectingflow through said control line and said second oil flow line, said valveconnecting said first oil flow line to said oil exit line and preventingsaid control and second oil flow lines from being connected to any otherlines when said inlet is open, and said valve connecting said secondflow line to said oil exit line'and said control line to said vent lineand preventing said first oil flow line from being connected to anyother line when said inlet is closed.

9. A control circuit for isolating a multi-stage coinpressor having aninlet and outlet, a discharge line com 9 necting said outlet to areceiver, said receiver having an oil sump therein, a, controlvalvehaving a first oil flow line connected to said oil sump anda-conduit1connected to said receiver, sensing meansconnected to aportion of said compressor intermediate said inlet and outlet and tosaid valve to cause said valve to assume a first or a second positioni'n'response, to pressure variations in said compressor portionresulting from the opening or closing of said inlet, a second oil fiowline connecting said discharge line to said valve, an ,oil flowexit lineconnecting said valve toroil injectingmeans, said oil injecting meansoperatively connected to said compressor for injecting oil into saidcompressor, a control line connected to said discharge line and to saidvalve, a vent line operatively connected to said control line by saidvalve wherein said vent line has a restrictive opening at the endthereof remote from said valve whereby the pressure therein is slowlyvented to a lower pressure, said vent line having valve meansintermediate its ends connected to said discharge line for closing saiddischarge line in response to flow of a pressurized medium therethroughat a pressure above said lower pressure without affecting flow throughsaid control line and said second oil flow line, said control valveconnecting said first oil flow line to said oil exit line and preventingsaid control and second oil flow lines from being connected to any otherlines when said control inlet is open, said valve connecting said secondflowline to said oil exit line and said control line to said vent lineand preventing said first fiow line from being connected to any otherline when said inlet is closed and said exit oil flow line having aportion with means for cooling oil flowing therethrough which portion isconnectible to said exit line by means responsive to the temperature ofthe oil flowing from said valve.

10. A control circuit for isolating a multi-stage com- A pressor havingan inlet and outlet, a discharge line connecting said outlet to areceiver, said receiver having an oil sump therein, a control valve,sensing means connected to a portion of said compressor intermediatesaid .inlet and outlet and to said control valve to assume a first or asecond position to cause said valve in response to pressure variationsin said intermediate portion resulting from the opening or closing ofsaid inlet, a first oil flow line connecting said valve and said oilsump, a second oil flow line connecting said discharge line to saidvalve, said valve having an oil flow exit line, a control line connectedto said discharge line and to said valve, a vent line operativelyconnected to said control line by said valve wherein said vent line hasa restrictive opening at the end thereof remote from said valve wherebythe pressure therein is slowly vented to a lower pressure,'said ventline having means intermediate said valve and said restrictive openingconnected to said discharge line for closing said discharge line inresponse to flow of a pressurized medium therethrough at a pressureabove said lower pressure without aifecting flow through said controlline and said second oil flow line, said valve connecting said first oilfiow line to said oil exit line and preventing said control and secondoil flow lines from being connected to any other lines when said inletis 4 open, said valve connecting said second flow line to said oil exitline and said control line to said vent line and preventing said firstoil flow line from being connected to any other line when said inlet isclosed, an auxiliary oil flow line connected to a portion of saidreceiver and to valve and said intermediate portion of said compressaidvalve, an auxiliary oil flow exit line connected to said sor, and saidvalve connecting said auxiliary oil flow line to said auxiliary oil flowexit line only when said inlet is open.

11. A control circuit 'for isolating a two stage compressor having aninlet and outlet with an intermediate receiver therebetween with saidoutlet being connected to .8 discharge line having a high pressuremedium flowing "10 therethrough to areceiver, said receiver having'anoil sump therein, a control valve, sensing means connecting saidintermediate receiver to said control valve to cause said valve to movetorone of two positions in response to pressure variations 'in saidintermediate receiver resulting from the, Opening or closing of saidinlet, a first oil flow line connecting said valve and said oil sump, ,asecondoil flow line connecting said discharge line to said valve,an oilflow exit lineconnecting said valve to oilinjecting means, said oilinjecting means opera- .tively connected to said compressor forinjecting oil into said compressor, a control line connected to saiddischarge line and to said valve, a vent line operatively connected tosaid control line by said valve vwherein said vent line has arestrictive opening in the end thereof remote from said valve wherebythe pressure therein is slowly vented to the atmosphere, said vent linehaving means intermediate the ends thereof connected to said dischargeline for closing said discharge line in response to flow of apressurized medium therethrough at a pressure above atmospheric pressurewithout affecting flow through said control line and said second oilflow line,

. said valve connecting said first oil flow line to said oil exit lineand preventing said control and second oil fiow lines from beingconnected to any other lines when said inlet is open, and said valveconnecting said second flow line to said oil exit line, and said controlline to said vent line and preventing said first oil flow line frombeing connected to any other line when said inlet is closed.

12. A control circuit for isolating a two stage compressor having aninlet and outlet with an intermediate receiver thereinbetween with saidoutlet being connected by a discharge line having a high pressure mediumflowing therethrough to a receiver having an oil sump thereincomprising, a control valve, sensing means connecting said intermediatereceiver to said control valve to condition said valve in one of twopositions in response to pressure variations in said intermediateportion resulting from the opening or closing of said inlet, a first oilflow line connecting said valve and said oil sump, a second oil flowline connecting said discharge line to said valve, an oil flow exit lineconnecting said valve to means for injecting oil into said compressor, acontrol line connected to said discharge line and to said valve, a ventline operatively connected to said control line by said valve whereinsaid vent line has a restrictive opening in the end thereof remote fromsaid valve whereby the pressure therein above atmospheric pressure isslowly vented to the atmosphere, said vent line having meansintermediate the ends thereof connected to said discharge line forclosing said discharge line in response to flow of a pressurized mediumtherethrough at a pressure above atmospheric pressure without affectingflow through said control line and said second oil flow line, said valveconnecting said first oil flow line to said oil exit line and preventingsaid control and second oil flow linesfrom being connected to any otherlines when said inlet is open, and said valve connecting said secondflow line to said oil exit line, said control line to said vent line andpreventing said first oil flow line from being connected to any otherline when said inlet is closed, an auxiliary oil flow line connected toa portion of said receiver other than said oil sump and said valve, anauxiliary oil flow exit line connected to said valve and saidintermediate receiver portion of said compressor, and said valveconnecting said auxiliary oil flow line to said auxiliary oil flow exitline only when said inlet is open.

13. A control system comprising a compressor with an inlet and adischarge line, said discharge line connects said compressor to areceiver for conducting a high pressure medium therethrough to saidreceiver, said receiver has an oil sump therein, a discharge valveintermediate said discharge line and said receiver, sensing meansconnecting said compressor to a control valve to cause said 11 controlvalve to assume one of two positions, said control valve having an oilexit linetherefrom, said control valve in one position having a firstoil flow line connecting said oil sump of said receiver to said oil exitline, said control valve in saidsecond position'connecting a second oilline from said discharge line to said exit line, and simultaneouslyconnecting a control line from said discharge line to a vent linemounted in said control valve, said vent line is operatively connectedto'said discharge valve for biasing said discharge valve to a'closedposition when said control valve is in its second operative posi- 12tion, said vent line is further connected to a restrictive opening toatmosphere, said control valve in said second position disconnects thecommunication between said first oil fiow line and said sump as wellas-between said dis- 6 charge line with said compressor.

References Cited in-the file of 'this patent UNITED STATES PATENTSAikman- Nov. l, 1938 2,279,431 Aikrnan Apr. 14, 1942 Wrrrn STATES PATENTFFICE QRTEFMATE F CQECTWN Patent Noe 297 039 March 28 1961 I Willard E.Green et a1.

It is hereby certified that error appears in the above numbered patentrequiring oorree'tion and that the said Letters Patent. should read ascorrec'bed belowm Column 9,, line 30* after "first," insert oil line 67,strike our "valve said intermediate portion of said c0mpres" and insertthe same after "said", second occurrence in line 68 same column Signedand 'hhis 10th day of October 1961.,

I (SEAL),

Attest:

ERNEST W. swmra I DAVID L. LADD Arresting Officer I Commissioner ofPatents USCOMM-DC-

